1. Technical Field
This invention relates to extruded earplugs for dampening airborne sound, and a method for producing such earplugs.
2. Background Information
Earplugs designed to be inserted into a person""s ear canals to dampen sound and prevent the entry of foreign matter are known in the art. Historically, these earplugs were manufactured from fibrous materials such as cotton. In more recent times, earplugs have been produced from polymer based materials, which tend to be more durable than the fibrous materials formerly used. One conventional method for making polymer-based earplugs is by die cutting plugs from sheets of cellular material such as vinyl or polyurethane foam. Such die cut plugs are usually cylindrically shaped in order that the earplugs can readily conform to the shape of a human ear canal. As a result, the amount of material waste in die cut plug production tends to be great (i.e., on the order of xc2xd of the foam web material) because the web between cut cylindrical earplugs cannot be used. The material used is often not recyclable, therefore, disposal of the waste material can represent a significant manufacturing expense. In addition, earplugs produced by this method have cut cells along their cylindrical surfaces. As a result, they have a rough surface which can be uncomfortable to the wearer and harbor dirt. These earplugs can also be difficult to insert into a wearer""s ear canals because they tend to lack longitudinal rigidity.
Another method for producing polymer-based earplugs is by molding them to the desired shape. For example, U.S. Pat. Nos. 4,774,938 and 3,872,559, both to Leight, disclose earplugs molded from polymer-based materials. Molded earplugs can be manufactured so that they are specially shaped and covered by a protective skin, enhancing their comfort and fit. However, the process of molding earplugs tends to be slower and more capital intensive than die cutting due to the large number of molds required. In addition, molded earplugs may be relatively difficult to insert into a user""s ears due to the fact that the polymer materials from which they are manufactured tend to lack longitudinal rigidity.
Attempts have been made to provide earplugs having sufficient longitudinal rigidity to allow them to be easily inserted into the ears and sufficient compressibility to allow snug yet comfortable wearer fit. For example, multi-component earplugs having a compressible element and a more rigid element are taught by U.S. Pat. No. 5,188,123 to Gardner, and U.S. Pat. No. 4,434,794 to Leight. Because the rigid and compressible elements of those earplugs must be individually manufactured and then joined together, their production processes tend to be slower and more costly than those for die cut earplugs.
U.S. Pat. No. 5,573,015 to Williams attempts to overcome some of the aforementioned drawbacks through the provision of a composite extruded earplug having a relatively soft sheath component surrounding a relatively rigid core component. The core component is provided to improve the longitudinal stiffness of the earplug, while the sheath component provides resiliency and user comfort. The composite aspect of this device, however, tends to disadvantageously complicate and/or increase the cost of the earplug. The thermoplastic elastomer of Williams"" device also tends to be disadvantageously expensive. In addition, the relatively stiff core may impinge on a user""s ear canal during insertion to cause user discomfort. Such a device also may be difficult to sufficiently compress for easy insertion into the user""s ear canal.
Thus, a need exists for a readily manufacturable and inexpensive sound dampening earplug providing the requisite compressibility for easy ear insertion, along with comfortable fit.
According to the present invention, a method is provided for fabricating an earplug. The method includes using an extruder having a die to extrude a monolithic body of foamed elastomeric thermoplastic material about 10 to 20 millimeters in diameter. The extrudate is then cut into discrete pieces about 10-35 millimeters in length to form individual earplugs.
In another aspect of the invention, an earplug sized and shaped for being received in the human ear canal is provided. The earplug includes an extruded monolithic body of foamed elastomeric thermoplastic material about 10 to 20 millimeters in diameter having a length of about 10-35 millimeters.
A further aspect of the present invention includes a monolithic earplug formed by the process of disposing a PVC-based material within an extruder under heat and pressure and incorporating a blowing agent into the material. The material is then extruded in a longitudinal direction from a die into an ambient environment wherein the blowing agent foams the extrudate, the extrudate having a transverse cross-sectional dimension of about 10 to 20 millimeters. The extrudate is cut at a 90 degree angle to the longitudinal direction, as it emerges from the die, prior to substantially complete cooling and expansion thereof. A convex, skinned surface is then formed at the cut ends as the extrudate subsequently expands and cools to form a monolithic earplug. The earplug has a density of about 6 to 12 pcf (96 to 192 kg/m3) and a rate of recovery from 80 percent compression sufficient to recover about 90 percent or less of its initial transverse cross-sectional dimension in 45 seconds, and after being compressed under a 5 pound weight for 6 seconds, to recover about 90 percent or more of its initial transverse cross-sectional dimension in 90 seconds. The use of such inherently-formed convex surfaces tends to aid insertion of the earplugs, without requiring any additional shaping operations. Provision of a skin on the ends, as well as the sides, of the earplugs advantageously tends to enhance the ability of the plug to block sound and improves the cleanliness due to the substantial elimination of open cells.
The monolithic structure forming the earplug is preferably capable of being compressed or deformed by hand down to about 20-50% or less of its original diameter. The slow recovery from compression facilitates ear insertion, while the tendency to return to its original dimensions advantageously serves to achieve a snug fit within the wearer""s ear.